The present invention relates to a method for the cooling of targets in sputtering sources as well as a cooling device for targets of sputtering sources with a target and with through which flow cooling agents.
When sputtering targets with sputtering sources, in particular when using so-called high rate sources such as magnetron sputtering sources, the problem is encountered of recognizing in time when the target has been consumed. If the plasma process is not interrupted in time, the target erodes through whereby an opening is created which exposes the rearward constructional elements of the magnetron source facing the plasma. This leads to a joint erosion of construction material which means as a rule an unacceptable contamination of the high purity layer to be generated. A breakthrough would have even more serious consequences for the cooling device whereby cooling medium penetrates into the process chamber. This leads to a destruction of the substrates as well as to complete failure of the installation and concomitant high expenses.
It is known that in the case of cathode sputtering installations the so-called targets must be cooled to achieve optimum operating capacity during sputtering of the targets. This cooling can be direct or indirect in that with the former the target can be brought into direct contact with the coolant liquid, e.g. water, or in the case of the latter, indirectly via an intermediate wall. The heat to be carried off can consequently either be carried off through heat transmission directly to the cooling medium in the case of direct cooling or through heat conduction through a wall in the case of indirect cooling.
It is further known, that with direct cooling the target mounting must be constructed especially carefully due to the danger of leaks.
With indirect cooling the cooling medium flows through cooling channels disposed in the interior of a back plate. This cooling method is without problems in terms of leakage, however it is significantly less effective with respect to cooling effect than direct cooling.
To circumvent the disadvantages of direct cooling and those of indirect cooling as well, it has also become known to implement the back plate, as in the case of direct cooling, with channels that are open toward the rear surface of the target and to close off these channels by a flexible foil, preferably comprising a metal, toward the outside in a liquid-tight manner. In operation the liquid pressure in the cooling channels causes the flexible metal foil to be pressed against the rear surface of the target and in this manner, heat transmission is significantly improved through the increase of heat conduction. See: J. Vac. Sci. Technol. A2(3), July-Sept. 1984 "Cathode cooling apparatus for a planar magnetron sputtering system" by M. R. Lake and G. L. Harding as well as "Planar Magnetron Zerstaubungsquellen" by Dipl.-Ing. Urs Wegmann, Balzers Fachbericht, BB 800 014 DD 8102.
In the Balzers report it is shown what the so-called removal profiles of targets generated by erosion look like. In the center of the erosion zone of the target a V-form depression originates. The target material, in other words, is not eroded uniformly. For the purpose of utilization of the expensive target materials however, one goes to the limit without risking a breakthrough of the target due to the erosion against the back plate.